2. amps-preamps
  3. 166258-110858

Detecting “Dirty” Power

I bought a used BHK 250 still under warranty. It is plugged into a Denali S power conditioner.  I heard a hum coming from the area around the tubes.  I cannot hear it from my sitting position and it doesn’t effect SQ, but I want it gone.  

I sent it to PS Audio; they tell me there is no hum and sent it back. They implied I mostly likely have a power problem and recommended some troubleshooting steps.  I unplugged everything from the 250 and plugged it straight into the PS Audio receptacle.  The hum is still there, but it is not as pronounced.  A P15 power regenerator might fix the problem, but I want to know if I have a power problem before I do anything.

How can I determine the quality of the power coming into my house and out of the receptacle? FYI, the Denali is plugged into a PS Audio receptacle/dedicated 20 amp line.  I have a whole house generator w/ transfer switch and whole house surge protector. 
128x128oldschool1948
vinylzone
288 posts
 
I don't know about the first link.  It won't block dc offset, and makes some "interesting" claims.  The AVA is what you should try.  Alternatively, Emotiva makes one too:  

https://emotiva.com/collections/accessories/products/cmx-2

I haven't tried it yet, but was going to order one shortly.  Both that and the AVA should work if the problem is indeed dc offset.
gs5556
1,234 posts
 
Start at step one: lift the ground of the amp by using a two prong cheater plug. If the hum goes away then it’s a ground loop.
oldschool1948's avatar
oldschool1948 OP
500 posts
 
I unplugged everything but the 250 and changed power cords.  Slight hum is still there.  I ordered the HumDinger.  I'll follow-up after I try it.
dletch2
455 posts
 
The Humdinger fixes transformer hum. You said the hum was near the tubes. If that is the case, it will not fix it.
gloriousunicorns
16 posts
 
Hey oldschool, I also have a BHK 250 and BHK pre like you do. When used together, they are extremely quiet. But when I used the BHK 250 with other pre amps and DAC’s I sometimes got a little noise. Using the XLR connection when I could eliminated that. My BHK 250 was always dead quiet with XLR. 
Also, try a different set of tubes. Even if the tubes are new, they can be bad. It might not even be both tubes, just one tube humming but you can’t tell. So if you have another set of tubes to throw in, give it a shot. And try tube dampers if you can. I have tube dampers (little silicone rings) and they made a small improvement on the tubes in my BHK pre. 
And just a few basic things, but like another poster suggested, try a cheater plug. And make sure the little panel that covers the tubes is screwed down tightly. If that metal panel is a little loose, that can be contributing to the hum... And although this last suggestion isn’t very practical, if you can bring the amp to another location, ie friends house or workplace, plug it in there and see if there’s still a hum. The BHK 250 is a little heavy though and not something you wanna carry around town. 
I’m not saying that dirty power isn’t causing the humming but I’m just suggesting things you can do before you go down the rabbit hole of power conditioning and noise blockers. Good luck. 
More to discover